As window glass for an automobile, laminated glass having two glass plates bent into a predetermined shape and an interlayer interposed between the two glass plates has been widely used. The two glass plates have the same glass composition and the same plate thickness from the viewpoint of the cost. The interlayer is constituted by a resin such as polyvinyl butyral (PVB) and prevents the broken glass from flying.
As a forming method of bending glass plates into a predetermined shape, commonly employed is a gravity forming method of placing the glass plates on a ring-shape lower mold (ring mold) supporting the glass plates from below and passing them through a heating furnace to heat and soften the glass plates and bend the glass plates by gravity into shape along the ring mold. A pressing method of sandwiching the glass plates preliminarily formed by gravity between the ring mold and a press mold, followed by pressing for main forming may also be employed.
In such a forming method, it is economically efficient to place the two glass plates overlaid each other on the ring mold and bending them simultaneously. In such a case, between the two glass plates, a release agent containing a ceramic powder is preliminarily applied.
In recent years, thickness reduction of laminated glass has been studied for the purpose of weight saving of an automobile (for example, Patent Document 1). Patent Document 1 proposes to make the glass plate on the car exterior side thicker than the glass plate on the car interior side, considering a collision of flying objects such as small stones from outside with the automobile.
Window glass for an automobile is formed in a convex curved shape toward the car exterior side at the time of attachment to a vehicle. In a case where the glass plate on the car exterior side is thicker than the glass plate on the car interior side, a thick glass plate and a thin glass plate are overlaid in this order on the ring mold, followed by heating and softening to bend them into a downwardly convex shape.